The present invention relates to the field of capacitive sensing, and in particular to capacitance measurement based displacement and proximity sensing, for example to detect when an object, such as a user's finger, presses on a moveable surface and when an object, such as a user's finger, approaches the moveable surface.
Capacitive sensing techniques have become widespread for providing touch-sensitive inputs, for example in computer tablets, mobile phones, and in many other applications. Touch sensitive input devices are generally perceived to be more aesthetically pleasing than input devices that are based on mechanical switches. Nonetheless, the present inventors have recognised there are still situations in which a user-interface that is responsive to mechanical input may be desired. In particular, the inventors have recognised there are situations in which there is a desire to measure the physical displacement of a displacement element, for example to provide the equivalent of a “click” when navigating a cursor across a display screen using a touch sensor. Furthermore, the inventors have recognised it can be desirable to provide such functionality using capacitive sensing techniques rather than mechanical switching techniques, for example because capacitive sensing techniques typically provide for more reliable sensors as they are less prone to mechanical wear.
One issue with using capacitive techniques for sensing the displacement of an element is the potential for the presence of whatever is causing the displacement, such as a user's finger, to affect the capacitance measurements in addition to the effect of the displacement itself. Capacitive-based capacitive sensors can be designed to reduce sensitivity to approaching objects to help avoid this issue. However, the inventors have further recognised there can be situations in which proximity detection may be desired in conjunction with displacement detection. For example, there may be situations in which it is desirable to detect when an object is approaching a capacitive sensor prior to any displacement occurring, for example to configure an apparatus being controlled by the capacitive sensor into a particular mode in expectation of a displacement. Alternatively, there may simply be a desire to sense the displacement of a surface and the proximity of an object over the surface for independent reasons.
Thus, there is therefore a desire to provide apparatus and methods for sensing when there is a displacement of a surface as well as when there is an object in proximity to the surface. In this regard, it will be appreciated that the reasons why there is a desire for proximity and displacement to be detected will be different in different scenarios and the particular reasons for detecting both proximity and displacement are not significant to the principles underlying the detection techniques described herein.